1. Field of the Invention
The present invention relates to a method and apparatus to improve storage capacity of a hard disk drive, and, more particularly, to a method and apparatus to perform write reordering.
2. Description of the Related Art
FIG. 1 is a view depicting a conventional write reordering method.
Referring to FIG. 1, after data 1, 2 and 3 are received from a host, the data 1 among the received data is written, and the data 2 and 3 remain in a state in which they are ready to be written. At this time, an access time when the data 2 and the data 3 gain access to several positions of a surface of the disk in which the data is to be written is computed. This access time is the sum of a seek time (i.e., the time required for a head to vertically move tracks) and a sector arrival time (i.e., the time required for the head to horizontally move tracks). The seek time is determined by a moving speed of the head, while the sector arrival time is determined by a rotating speed of the disk.
A time required to move the head from the sector into which the data 1 is written to the sector into which the data 2 is to be written in a direction that is perpendicular to the tracks will be referred to as ST2, while a time required to move the head from the moved position where the data 2 is to be written in a direction that is horizontal to the tracks will be referred to as SA2. A time required to move the head from the sector into which the data 1 is written to the sector into which the data 3 is to be written in a direction that is perpendicular to the tracks will be referred to as ST3, while a time required to move the head from the moved position where the data 3 is to be written in a direction that is horizontal to the tracks will be referred to as SA3. Accordingly, the access time AT2 when the head gains access to the position where the data 2 is to be written from the current position is ST2+SA2, while the access time AT3 when the head gains access to the position where the data 3 is to be written from the current position is ST3+SA3. In view of the rotation of the disk and a relationship of AT2 being greater than AT3, writing the data 3 before writing the data 2 is effective. In this case, according to the conventional write reordering method, the write order is reordered in order of the data 1, then the data 3 and then the data 2.
When the head is moved, an accelerating section, a constant velocity section and a decelerating section operate. Therefore, a seek speed is not increased in relation to the moving distance of the head. Specifically, if a ratio of the accelerating section and the decelerating section is large, the seek speed is slow. If a ratio of the constant velocity section is large, the seek speed is fast. A conventional hard disk drive stores seek times associated with every moving distance. As such, a problem exists in that when the moving speed of the head is varied by any cause, the stored seek times are not consistent with each other. In addition, in the case in which write reordering is performed, an incidence of inconsistent seek times may significantly reduce a performance of the hard disk drive.